Seeds leak a wide range of compounds when imbibed in water including carbohydrates, proteins and inorganic ions (Samad and Pearce, 1978, J. Exper. Botony, 29:1471-1478) and larger intracellular substances such as starch, grains and protein bodies (Spaeth, 1987, Plant Physio., 85:217-223). Differential leakage of specific compounds has been associated with seed viability in some species. The percentage of water soluble carbohydrates was negatively correlated with germination in carrot (Daucus carota L.) (Dadlani and Agrawal, 1983, Scientia Hort., 19:39-44). Fructose, glucose, sucrose, maltose, raffinose and stachyose were identified in the leachate from non-viable rape (Brassica napus L.) seeds (Takayanagi and Murakami, 1969, Proc. Internat. Seed Testing Assoc., 34:243-252). Viable seeds leaked only trace amounts of fructose and glucose. Artificially aged soybean (Glycine max L. Merr) seeds were observed to leak higher amounts of compounds that absorbed light at 260 nm than non-aged seeds (Schoettle and Leopold, 1984, Crop Sci., 24:835-838).
Phenolic compounds have been found in seeds. Sinapine, the choline ester of sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid) (Austin and Wolff, 1968, J. Agr. Food. Chem., 16:132-135), has been found among various species of Brassicaceae (Cruciferae) (Schultz and Gmelin, 1952, Z. Naturforschung, 7b:500-508), and is the main phenolic constituent of rape seed occurring at levels from 1.0-2.5 percent dry matter (Blair and Reichert, 1984, J. Sci. Food. Agri., 35:29-35). The compound is fluorescent under UV light and becomes yellow at high pH (&gt;10). Hydrolysis products of sinapine are sinapic acid and choline which are metabolized during germination (Tzagoloff, 1963, Plant Physio., 38:202-206).
Non-viable or deteriorated seeds have been reported to leak more solutes when placed in water than viable or vigorous seeds (Simon and Harun, 1972, J. Ex. Botany, 23:1076-1085; Leopold, 1980, Plant Physio., 65:1096-1098; Powell and Matthews, 1981, J. Ex. Botany, 32:1045-1050). Aged, damaged, or non-functional cellular membranes (Simon and Harun, 1972, supra; McKersie and Stinson, 1980, Plant Physio., 66:316-320; Murphy and Noland, 1982, Plant Physio., 69:428-431) and cellular rupture caused by imbibition damage (Powell and Matthews, 1979, J. Ex. Botany, 30:193-197; Duke and Kakefuda, 1981, Plant Physio., 67:449-456) have been suggested as major causes.
Among the solutes leaked from seeds of various species are; free amino acids (Harman and Granett, 1972, Physiol. Plant Path., 2:271-278), proteins (McKersie and Stinson, 1980, supra), sugars (Takayanagi and Murakami, 1969, supra), and phenolics (Samad and Pearce, 1978, supra). Ions and inorganic compounds of potassium, phosphate, and magnesium are also leaked (Simon and Harun, 1972, supra; Samad and Pearce, 1978, supra; McKersie and Stinson, 1980, supra). The two most common methods of measuring seed leakage are electrical conductivity and light absorption at specific wavelengths (Harman and Granett, 1972, supra; Duke, Kakefuda, and Harvey, 1983, Plant Physio., 72:919-924; Hepburn, Powell, and Matthews, 1984, Seed Sci. & Tech. 12:403-413).